This invention concerns fluid flow meters of the type used to measure various flow parameters as fluid flow velocity and mass rate of flow.
It has long been known to measure fluid flow velocity in a flow stream by disposing a drag body or target in the flow stream and measuring the drag force exerted on the body by the fluid flow by various arrangements. The drag force varies with the velocity of flow and thus provides a measure of the average fluid flow velocity in the stream.
This approach, while simple, has the disadvantage of yielding an analog output signal which varies nonlinearly with fluid flow. That is, the drag force varies with the square of the velocity of fluid flow. Also, the analog form of the output signals is relatively inconvenient for handling in digital signal processing circuitry.
It has also been known in the prior art to utilize flow meters which have included means for causing oscillation or turbulence of the fluid in a conduit, the frequency of which is proportional to the fluid velocity. The oscillations are measured by various arrangements, the frequency of which are related back to the flow velocity. This, of course, produces a relatively large pressure loss due to the requirement for substantial turbulent flow about the body.
A typical such arrangement is disclosed in Jannsen et al U.S. Pat. No. 3,863,501.
It is accordingly the object of the present invention to provide a simple drag force measuring flow meter in which the output signal is in digital form and in which there is established a linear relationship between the output signal and the flow rate.